Listeriosis is a foodborne illness primarily caused by ingesting food contaminated with a bacterium called Listeria monocytogenes. Approximately 150 Canadians are infected with listeriosis each year. Though rare, listeriosis can sometimes lead to death, especially in people with weakened immune systems, such as the elderly, pregnant women (and their fetuses), and very young children.

How to avoid listeriosis?

Listeriosis is not contracted by coming into direct contact with an infected person. Nor is contamination visible to the naked eye. Infection can occur after eating contaminated food or after coming into contact with a contaminated surface or object such as a cutting board or knife (cross-contamination).

Listeria bacteria are very resistant and can survive for many years in the open air, including in cold temperatures. Listeria proliferates in refrigerators and survives in freezers. However, it does not tolerate heat and is easily destroyed by the high temperatures achieved through proper cooking. Raw foods are therefore most vulnerable to Listeria contamination.

Foods at greater risk of Listeria contamination:

  • Improperly washed fruits and vegetables
  •  Unpasteurized dairy products
  •  Raw milk cheeses
  • Raw meat (tartar, carpaccio, etc.)
  •  Deli meats (salami, prosciutto, etc.)
  • Smoked and raw fish
  • Seafood

It’s worth noting that listeria monocytogenes is not only found in food, but also widely throughout our environment: in untreated water, soil and vegetation as well as in human and animal feces.

Detecting food contaminated with listeria monocytogenes is very difficult because the food shows no signs or change in appearance, taste or smell. The incubation period of listeriosis also varies greatly – from 2 days to 2 months. What’s more, its symptoms are similar to those of most types of food poisoning.

Precautions and hygiene measures

The best way to prevent listeriosis is by practicing good hygiene and by following basic food handling and safety rules:

• Regularly clean and disinfect refrigerators.
• Be careful when handling cooking juices and meat packages containing blood.
• Wash your hands thoroughly with soap and water before and after handling food, before and after touching an animal or going to the bathroom.
• Disinfect work surfaces and utensils that have come into contact with raw food.
• Consume food quickly after opening the package and always respect the expiry date.
• Do not thaw food at room temperature; thawing it in a refrigerator or microwave are a safer bet.
• Always cook ground meat thoroughly.
• Wash fruit and vegetables carefully with potable water.
• Clean work surfaces and utensils that have come into contact with raw foods to avoid contaminating other types of food. Always use soap and water to thoroughly clean utensils and cutting boards that have come into contact with raw meat or fish.